Development of effective vaccines against respiratory viruses requires a thorough understanding of the immunological response to individual proteins. Recombinant vaccinia viruses have been constructed that express individual influenza virus genes. Tissue culture cells infected by vaccinia recombinants expressing haemagglutinin (HA-VAC) or nucleoprotein (NP-VAC) synthesized authentic influenza polypeptides which were expressed on the cell surface thd which were recognized by anti-influenza A virus cytotoxic T lymphocytes (CTL) in a H-2 restricted manner. Animals vaccinated with HA VAC recombinants produced antibodies against HA (anti-HA) and were protected against subsequent intranasal challenge with influenza virus of the homologous subtype. Mice immunized with HA-VAC or NP-VAC were primed for secondary anti-HA or anti-NP CTL responses, respectively. Anti-HA CTL were mostly subtype specific while anti-NP CTL were strongly crossreactive among all influenza A virus subtypes. A cDNA copy of the glycoprotein G gene of respiratory syncytial virus has been inserted into the vaccinia virus genome. A glycosylated protein of 84 kD was synthesized and immunoprecipitated with specific antiserum. Transport to the cell surface was demonstrated by immunofluorescence.